There are several commercial approaches for joining components for stable working operation at high-temperature. One is “brazing” and another is thermocompression bonding. In the brazing approach, a mixture of metals at the eutectic composition is applied between the two members to be joined. The metals are aggressive chemically and the composition of the active components of an electrical element (e.g., the thermoelectric materials) can be significantly degraded by chemical interaction and interdiffusion with the braze. Also, the eutectic compound for the most common braze (aluminum-silicon eutectic) is only stable to about 660° C., which limits the useful temperature range available to many applications. Also, voids can form because of chemical interdiffusion between the components and the braze, and embrittled layers with poor mechanical properties can result. To successfully pursue this brazing approach, usually a more complicated, multi-layer solution composed of adhesion layers, diffusion barriers, and fluxes for the braze is utilized.
Thermocompression bonding uses thin gold layers applied to the two components to be joined. The two gold layers are placed in contact and heated to high-temperature to drive the mutual self-interdiffusion of the two gold layers into one monolithic gold layer. Gold does not oxidize at standard temperature, pressure and common lab environments, so thermocompression bonding can result in a low resistance electrical contact. However, gold is known to rapidly diffuse along all the surfaces and deeply into electrical components, such as thermoelectric materials. The deep diffusion of gold is known to poison thermoelectric materials and degrade thermoelectric device performance.
A method of forming low electrical resistance junctions that are strong and stable to elevated temperatures such as 800 to 900° C. may be useful.